There has hitherto been known a multi-usable thermal transfer ink sheet in which on a foundation is provided a heat-meltable thermal transfer ink layer containing a heat-meltable substance and a pigment as main ingredients. Such an ink sheet is adapted to transfer the thermal transfer ink layer in portions in terms of the thickness thereof onto a receptor every time the ink layer is heated by a thermal head.
As far as a thermal transfer ink sheet of this type is used in printing with a common thermal transfer method (hereinafter referred to as "direct thermal transfer method") wherein a thermal transfer ink sheet is superimposed on a receptor and ink of the ink sheet is directly transferred onto the receptor, such a thermal transfer ink sheet has been capable of being reused some times.
Recently, on the other side, there has been proposed a thermal transfer method called "indirect thermal transfer method".
This indirect thermal transfer method uses a device such as shown in FIG. 1. In FIG. 1, numeral 10 denotes a rotatable transfer drum of which the surface is composed of an elastic material of good releasing property such as silicone rubber or fluorine-containing rubber. Numeral 11 denotes a recording part which is arranged so that a thermal head 13 can press a thermal transfer ink sheet 12 against the transfer drum 10. The ink sheet 12 is moved in the direction indicated by an arrow as the transfer drum 10 rotates for recording. Numeral 14 denotes a transfer part which is arranged so that a receptor 15 can be pressed against the transfer drum 10 by means of a pressing roller 16. In printing the receptor 15 is moved in the direction indicated by an arrow.
The thermal head 13 heats the thermal transfer ink sheet 12 so as to soften or melt the ink thereof which is then transferred onto the surface of the transfer drum 10. While the transfer drum 10 and the ink sheet 12 are thus moved in the directions indicated by the arrows, respectively, the softened or molten ink is transferred onto the transfer drum 10 so as to form an inked image 17 thereon. The inked image 17 is moved to the transfer part 14 as the transfer drum 10 rotates, pressed against the receptor 15 there, and transferred onto the receptor 15 to form a final inked image 18.
The transfer drum 10 is always heated at about 60.degree. to about 80.degree. C. for ease of transfer of the inked image thereon onto the receptor 15.
The present inventors attempted to carry out multi-printing by using a multi-usable thermal transfer ink sheet of the aforesaid type in such an indirect thermal transfer method. As a result, it was found that multi-printing was difficult because of poor transferability of ink onto the transfer drum.
In view of the above-mentioned, it is an object of the present invention to provide a thermal transfer ink sheet capable of multi-printing even in the indirect thermal tranfer method.